Concerning licensing, I talked with MaximGB, and we agree on wanting people to use extensions like BrowseButton without any restrictions. Do you foresee any issues with just saying it's part of the public domain, or at the maximum giving it a BSD style license?

I could get Opera to work with BrowseButton if the button was explicitly created and added to the Panel's button bar through "button" config. I have updated the browser compatibility in the post to report this.

I tried to verify the IE7 issue. I added 20 files with no problem. How many files were you adding when it started to break for you?

When I right-click an element in your FileTreePanel it shows a context menu, but also shows the Firefox right-click menu. I don't know how easy or if is it even advisable to supress the Firefox right-click menu, what do you think?